A number of hydrocolloids, pectin, alginate, carrageenans, potato starch and carboxymethyl cellulose are negatively charged due to galacturonate (Pectin), α-D-mannuronate and α-L-guluronate (Alginate), sulphate groups (carrageenans), phosphate groups (potato starch) and carboxymethyl groups (carboxymethyl-cellulose). These substitutions have a profound influence on the functionality of the hydrocolloids in complex food matrices. Whereas pectin, alginate, potato starch and carrageenan are naturally occurring and are synthesized by plants and algae, carboxymethylcellulose is produced from cellulose by chemical treatment. Due to regulatory restriction and costs for approvals, only a few chemically modified hydrocolloids have been approved for use in foods.
A large number of food and feed products contain starch and therefore may be suitable for further processes like enzymatic modification. In particular, in the bakery process, control of starch retrogradation and recrystallization is of importance in slowing staling of bread.
Polysaccharide derivatives containing aldehyde groups and their use as paper additives are known in the art. For example, U.S. Pat. No. 4,675,394 describes polysaccharide aldehydes, such as starch, gum and cellulose aldehydes and their preparation by a non-oxidative method which involves reacting the polysaccharide base, in the presence of alkali, with a derivatising acetal reagent and then hydrolyzing the resulting acetal.
Oxidized saccharides, in particular oxidized polysaccharides, are useful as coupling agents in various technical fields, in particular in the pharmaceutical industry, where such compounds act to enhance the solubility and delivery of various pharmaceuticals. For example, US2006198819 describes a method for producing a conjugate of a glycoprotein having at least one terminal galactose or derivative thereof, and a protractor group covalently bonded thereto, the method including a step of contacting the galactose-containing glycoprotein with galactose oxidase to oxidise the galactosyll group. The conjugates are stated to have increased in vivo plasma half-life compared to non-conjugated glycoprotein.
U.S. Pat. No. 4,663,448 describes aldehyde-containing heteropolysaccharides, in particular starch ether derivatives, and their preparation using the enzyme galactose oxidase, in which the C-6 position of the glycoside unit is oxidised to the aldehyde functionality.
U.S. Pat. No. 6,265,570 describes stable, sold water soluble starch aldehyde compositions and methods for their preparation by preparing a converted starch acetal and hydrolysis of the acetal under acid conditions to form the starch aldehyde.
Chemical oxidation of polysaccharides such as starch to prepare aldehyde derivatives thereof is known in the art. For example, U.S. Pat. No. 7,247,722 describes preparation of polysaccharide aldehydes using selective oxidation using nitroxyl radical mediator, such as 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) radical.
WO 99/23240 describes a method for producing oxidised starch by using a reagent, such as TEMPO, which produces an oxoammonium ion, in conjunction with an oxidising enzyme, in particular an oxidase (such as laccase) or a peroxidase. However, in the process described in this document, it is the TEMPO which is the oxidising agent: the enzyme is used to regenerate the TEMPO to enable it to be used in catalytic quantities. Chemical oxidations of this type, however, often require harsh reagents and the regiospecificity of such chemical oxidations including the TEMPO method, is limited.
There is therefore a need for an oxidation method for sugars which oxidises alcohol functionalities in sugar molecules more selectively, in particular at the C-6 or C-5 positions of hexose and pentose rings respectively. Furthermore, there is a need for methods for performing such oxidation reactions using milder reagents.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.